The present invention relates to a reinforcement element with a sensor fiber, monitoring system utilizing the reinforcement element, and a monitoring method adapted for the system.
Reinforcement elements are widely used in structures of any kind. Typically, reinforcement elements are load bearing elements or, at least, load-sensitive elements of the structure. Therefore, reinforcement elements have been equipped with sensors to monitor the actual condition of structures or to detect creeping behavior resulting in changes of the structure or even in a loss of structural integrity. Such monitoring is especially important for protective structures like dykes, dams or the like since collapse of the structure may have severe or even catastrophic consequences.
A recent type of reinforcement elements are geotextiles. Geotextiles as such are known, e.g., from DE 197 46 052 C2. For example, geosynthetic clay proofing sheets without a monitoring function are mostly used at the present time for dyke renovations. These sheets can connect not filter-stable soil layers safe against erosion or may be used as a water-side sealing, but cannot be employed for dyke monitoring.
DE 195 06 180 C1 and DE 295 21 732 U1 describe a method and a device which makes it possible to check and monitor the condition of dykes, dams and weirs on the basis of distributed temperature measurement by means of a fiber-optic sensor cable. Laser radiation is coupled into the sensor cable, and on the basis of a transit-time and intensity evaluation of the Raman-backscattered laser radiation a distributed temperature measurement can be performed. When an anomaly in temperature distribution is detected, a dyke leakage is detected and the location of this anomaly can be determined.
Optical fibers as deformation sensors in geotextiles are offered by the company Polyfelt (www.polyfelt.com) with the product “Geodetect”. This geoplastic is based on what are known as fiber Bragg grating (FBG) sensors. These FBG sensors are chain sensors which can be incorporated into the fiber at specific local points and which possess a measurement length of a few millimeters. FBG sensors of this type carry out only point measurement and, therefore, do not give sufficiently reliable information on geomats laid over a large area. In other words, FBG sensors deliver only local information on the mechanical behavior but the deformation behavior of large measurement areas cannot be simply deduced therefrom.